Has there been a shift in the UK winter wheat yellow rust population? Recent Recommended List trial inspections in the North suggest there could have been. CPM speaks to the experts for their thoughts.
“It was always going to happen, it was just a question of when.” JOHN MILES
By Janine Adamson
As shared by AHDB at the beginning of April, signs of yellow rust have been identified on almost all Recommended List varieties classed as resistant at the young plant stage during trial inspections in the north of England, including some popular varieties.
AHDB says there are also initial hints of ‘something unusual’ starting to happen in other RL trial regions too.
Although the yellow rust pathogen population is diverse, past experience shows it’s not unexpected to detect new strains. However what’s concerning, says AHDB’s Mark Bollebakker, is these early observations suggest there may be a significant new strain, or strains, in the UK pathogen population which haven’t been seen before.
Equally, some varieties historically classified as susceptible at juvenile plant stage are currently relatively clean at the impacted trial sites. Again, this indicates a potential pathogen population shift which may have displaced some other yellow rust strains, adds Mark.
“The trials in question were at GS30 at the time of inspection, so adult plant resistance hadn’t kicked in. When it does – from stem extension onwards – these varieties may outgrow initial infection. However, it’s difficult to predict what will happen.”
FURTHER INSPECTION
AHDB has since sent samples to UKCPVS for testing to provide a better understanding of what’s being observed. In the meantime, Mark suggests farmers and agronomists inspect all varieties before final spray decisions and shouldn’t rely on the RL ratings until more is understood.
Agrii’s seed technical manager, John Miles, raises that historically speaking, it’s typical to see around 3-5 suspected incidences of varietal resistance being overcome each year. However, when these are investigated further, they often don’t transpire to anything. “It might be due to human error at drilling, for example, or a mix up with seed.
“But this year the numbers have continued to climb with the problem spreading further south as a gradual burn,” he explains. “It appears to be something different altogether, and due to it originating in the North, it’d indeed suggest a new race has been blown or carried in.”
According to John, this shouldn’t really be surprising. “Mother Nature has cooked up something new – it was always going to happen, it was just a question of when. The best case scenario will be it’s only the juvenile plant resistance mechanism which has been overcome.
“On the other hand, this could continue to build and have a significant impact. We have to wait and see; if we do lose that resistance mechanism which in many ways we’ve become reliant on, it’d be a shame,” he says. “Equally, it’s positive that so far it hasn’t built up quickly. If those varieties now take a bit of yellow rust, that’s a problem we can handle.”
Hutchinsons’ head of integrated crop management, David Howard, says agronomists in his teams are noting similar observations. “It’s not yet at a significant scale, but we’re certainly receiving more questions regarding unexpected varieties such as LG Typhoon and Champion (DSV), and less so for those which you’d assume to be susceptible like KWS Zyatt.”
He adds that in terms of crop management, this is could have implications on planned fungicide programmes and therefore adaptations may have to be made. “This season seems to be rust-heavy and we know it’s a disease which cycles quickly, but hopefully this means rust management is already front of mind for many growers.
“Although we’ve experienced cold weather during the winter and early spring, I don’t believe it’ll have been enough to fully knock the disease out of crops. Instead, cooler conditions will have extended the latency of yellow rust, therefore it could be in plants but not visible yet.”
David explains that even though conditions have been dry for some time (at the time of writing, mid-April), with heavy dews and crops rubbing together, risk remains high. “Don’t assume there’s no pressure, it’s certainly better to err on the side of caution.
“Equally, despite not observing the same levels of early brown rust as we saw last season, this disease still has the potential to explode later on.”
CONTROL OPTIONS
John reminds that although this potential shift in yellow rust pathogen population is undoubtedly interesting news for the industry, it remains a relatively easy disease to control with available chemistry. “With cost-effective options, namely tebuconazole, growers and agronomists should be able to successfully fight the pressure. We’ve seen this in the field, as growers continue to achieve success despite opting for what we’d deem ‘rusty’ varieties.
“Looking more broadly at disease, with brown rust becoming more prevalent, yellow rust is behind both that and septoria in terms of how challenging it is to control,” he comments.
But what do the breeders have to say on the matter? Limagrain’s Ron Granger reveals the firm’s plant pathologists and breeders are monitoring the situation closely. “As we’re currently uncertain how this will develop from the juvenile to the adult plant stage, vigilance is key to assess crops if early signs of rust do appear.
“What we do know is the levels of disease are unlikely to be uniform across all of these varieties, as those with more complex combinations of background resistance will likely show less symptoms.”
As recommended by AHDB, Ron concludes it’s important to observe all crops and seek advice from an agronomist regarding any adjustments to fungicide rates or timings.
This article was taken from the latest issue of CPM. Read the article in full here.
For more articles like this, subscribe here.
Sign up for Crop Production Magazine’s FREE e-newsletter here.
